1. Technical Field
The present disclosure relates to a workpiece cloth positioning guide device for a sewing machine, which projects a sewing reference mark onto an upper surface of workpiece cloth placed on a sewing bed of a sewing machine thereby to guide the positioning of the workpiece cloth in a sewing operation.
2. Description of the Related Art
In sewing workpiece cloth by a sewing machine, stitches are sometimes formed with a predetermined distance from an edge of the workpiece cloth or stitches previously formed on the workpiece cloth. There has conventionally been provided a device comprising a generally rectangular presser foot 100 as shown in FIG. 20, for example. In sewing, an edge 101a of workpiece cloth 101 is positioned relative to a side edge of the presser foot 100 so that, for example, the edge 101a of the workpiece cloth 101 corresponds with the side edge of the presser foot 100. When the workpiece cloth 101 is fed while the aforesaid state of the workpiece cloth 101 is maintained, stitches 102 are formed on the workpiece cloth 101 with the predetermined distance from the edge 101a of the workpiece cloth 101.
In another conventional example, for instance, stitches 107 previously formed on the workpiece cloth 106 are positioned relative to an outer circumference of a ring-shaped presser foot 105 in sewing as shown in FIG. 21. For example, the stitches 107 are positioned so as to lie adjacent to the outer circumference of the presser foot 105. When the workpiece cloth 106 is fed while the aforesaid state of the workpiece cloth 106 is maintained, stitches 108 are formed on the workpiece cloth 101 with a predetermined distance from the previously formed stitches 107.
On the other hand, Japanese Patent No. 2775961 discloses a sewing machine comprising a projector attached to a head of the sewing machine in order that stitches may be formed on workpiece cloth with a predetermined distance from an edge of the workpiece cloth. The projector has a light source, a liquid crystal panel and projector lens. The projector projects a linear sewing reference line serving as a mark to position an edge of the workpiece cloth.
However, as in the devices shown in FIGS. 20 and 21, the sewing machine head is located over the presser foot when the edge of the workpiece cloth or the previously formed stitches are to be positioned relative to the presser foot. As a result, the operator views the presser foot and the workpiece cloth from obliquely upward. In this case, the presser foot stands in the way of the operator's view. Moreover, the operator has difficulty in getting positions of the edge of the workpiece cloth and the previously formed stitches relative to the presser foot. Accordingly, it becomes difficult to position the edge of the workpiece cloth and the previously formed stitches accurately relative to the presser foot and further, to feed the workpiece cloth so that the edge of the workpiece cloth and the previously formed stitches are maintained at the positions. Thus, it is difficult for the operator to form stitches with a predetermined stitch interval relative to the edge of the workpiece cloth or previously formed stitches.
Furthermore, since the stitch interval depends upon the size of the presser foot, the stitch interval cannot be changed unless the presser foot is changed to another with a different size. This problem can be coped with by providing a plurality of differently sized presser feet and selecting a desired one. However, changing the presser foot is extremely troublesome for the operator, and providing a plurality of presser feet results in cost disadvantage. Furthermore, the number of presser feet to be provided has a definite limit. As a result, changing the stitch interval also has a definite limit, and the stitch interval cannot be changed to a desired value in many cases.
On the other hand, the sewing machine disclosed by Japanese Patent No. 2775961 comprises the projector which projects the linear sewing reference line serving as the mark to position the edge of the workpiece cloth. The sewing reference line is projected onto the sewing bed and a part of the upper surface of the workpiece cloth spaced away frontward from the needle drop point (needle hole of a needle plate). As a result, the sewing machine disclosed by Japanese Patent No. 277596 has a difficulty in forming stitches with a predetermined stitch interval being provided relative to the edge of the workpiece cloth including a curved one as in the case where a presser foot is used in the apparatus shown in FIG. 20.